Herzog Simone, Kaletsch Anke, Broeckmann Christoph
Institute for Materials Applications in Mechanical Engineering, RWTH Aachen University, Augustinerbach 4, 52062 Aachen, Germany.
Membranes (Basel). 2023 May 10;13(5):504. doi: 10.3390/membranes13050504.
The separation of oxygen from air by means of inorganic ceramic membranes requires gas-tight ceramic-metal joints that enable reliable permeation operation in the oxygen partial pressure gradient at 850 °C. Reactive air brazing is a promising method to solve this challenge. However, reactive air brazed BSCF membranes suffer from a significant strength degradation that is caused by unhindered diffusion from the metal component during aging. In this study, we investigated how diffusion layers applied on the austenitic steel AISI 314 influence the bending strength of BSCF-Ag3CuO-AISI314 joints after aging. Three different approaches were compared as diffusion barriers: (1) aluminizing via pack cementation, (2) spray coating with NiCoCrAlReY, and (3) spray coating with NiCoCrAlReY and an additional 7YSZ top layer. Coated steel components were brazed to bending bars and aged for 1000 h at 850 °C in air prior to four-point bending and subsequent macroscopic as well microscopic analyses. In particular, coating with NiCoCrAlReY showed low-defect microstructures. The characteristic joint strength was raised from 17 MPa to 35 MPa after 1000 h aging at 850 °C. In addition, the dominant delamination fracture between the steel and the mixed oxide layer, observed in the reference series with uncoated steel, could be replaced by mixed and ceramic fractures of higher strength. The effect of residual joint stresses on the crack formation and path is analyzed and discussed. Chromium poisoning could no longer be detected in the BSCF, and interdiffusion through the braze was effectively reduced. Since the strength degradation of reactive air brazed joints is mainly caused by the metallic joining partner, the findings on the effect of the diffusion barriers in BSCF joints might be transferred to numerous other joining systems.
通过无机陶瓷膜从空气中分离氧气需要气密的陶瓷 - 金属接头，以确保在850°C的氧分压梯度下可靠地进行渗透操作。活性空气钎焊是解决这一挑战的一种有前途的方法。然而，活性空气钎焊的BSCF膜会出现显著的强度退化，这是由于老化过程中金属成分不受阻碍的扩散所致。在本研究中，我们研究了涂覆在奥氏体钢AISI 314上的扩散层如何影响老化后BSCF - Ag3CuO - AISI314接头的弯曲强度。比较了三种不同的作为扩散阻挡层的方法：（1）通过包埋渗铝，（2）喷涂NiCoCrAlReY，以及（3）喷涂NiCoCrAlReY并附加7YSZ顶层。将涂覆的钢部件钎焊到弯曲棒上，并在850°C的空气中老化1000小时，然后进行四点弯曲以及随后的宏观和微观分析。特别是，喷涂NiCoCrAlReY显示出低缺陷的微观结构。在850°C老化1000小时后，特征接头强度从17 MPa提高到35 MPa。此外，在未涂覆钢的参考系列中观察到的钢与混合氧化物层之间占主导地位的分层断裂，可以被更高强度的混合和陶瓷断裂所取代。分析并讨论了残余接头应力对裂纹形成和路径的影响。在BSCF中不再检测到铬中毒，并且通过钎料的相互扩散得到了有效减少。由于活性空气钎焊接头的强度退化主要由金属连接部件引起，因此关于BSCF接头中扩散阻挡层效果的研究结果可能会推广到许多其他连接系统。
